The man who gave the Black Panther Party some of its first firearms and weapons training – which preceded fatal shootouts with Oakland police in the turbulent 1960s – was an undercover FBI informer, according to a former bureau agent and an FBI report.

One of the Bay Area’s most prominent radical activists of the era, Richard Masato Aoki was known as a fierce militant who touted his street-fighting abilities. He was a member of several radical groups before joining and arming the Panthers, whose members received international notoriety for brandishing weapons during patrols of the Oakland police and a protest at the state Capitol.

Aoki went on to work for 25 years as a teacher, counselor and administrator at the Peralta Community College District, and after his suicide in 2009, he was revered as a fearless radical.

But unbeknownst to his fellow activists, Aoki had served as an FBI intelligence informant, covertly filing reports on a wide range of Bay Area political groups, according to the bureau agent who recruited him.

That agent, Burney Threadgill Jr., recalled that he approached Aoki in the late 1950s, about the time Aoki was graduating from Berkeley High School. He asked Aoki if he would join left-wing groups and report to the FBI.

“He was my informant. I developed him,” Threadgill said in an interview. “He was one of the best sources we had.”